1. Field of the Invention
The present invention relates to a technique for displaying an image.
2. Description of the Related Art
In recent years, image display devices such as a TV receiver and PC monitor which include various display devices (for example, a liquid crystal display device) have been put into practical use. In general, in a liquid crystal display device, so-called “burn-in”, which cannot reproduce tone characteristics due to a charge bias, occurs when a DC voltage is kept applied between pixel and counter electrodes for a long period of time.
For this reason, the liquid crystal display device is driven as follows. That is, for example, an input image signal having a frame rate of 60 Hz is doubled to 120 Hz to define sub-frames, so as not to cause any charge bias. Then, the polarity of a signal voltage to be applied to liquid crystal for each sub-frame is periodically inverted with respect to a common electrode voltage (VCOM). In this case, a driving operation for inverting the polarity of a signal voltage to be applied to a liquid crystal for each sub-frame is called a sub-frame inversion AC driving operation.
On the other hand, in a hold type display device represented by a liquid crystal display device, when a following view of a moving object is made (a way of viewing a moving object while being followed by a line of sight in movie display), a motion blur according to a light output period is observed. As a technique for suppressing such motion blur, a “spatial frequency separation method” has been proposed. The “spatial frequency separation method” is a display method which concentrates spatial high frequency components involved in a motion blur on one sub-frame and reduces them in the other sub-frame. Thus, since spatial high frequency components are locally included in one sub-frame in an output image, a motion blur can be suppressed.
However, in the “spatial frequency separation method”, since different voltages are applied between sub-frames, an applied voltage is biased to one polarity, and burn-in is generated upon driving for a long period of time. For this reason, a technique for further suppressing a motion blur by reducing an increase in charge accumulated amount by correcting a driving waveform in the “spatial frequency separation method” according to an accumulated value of differences between sub-frames, that is, a charge accumulated amount has been disclosed (patent literature 1 (Japanese Patent Laid-Open No. 2009-042481)). Also, a technique for preventing an applied voltage from being biased by extending a polarity inversion driving period from a sub-frame unit to a frame unit has been disclosed (patent literature 2 (Japanese Patent Laid-Open No. 2008-064919)).
With the technique disclosed in patent literature 1, since an accumulated value of differences between sub-frames is stored, a charge accumulated amount can be estimated with high precision, while a frame memory is required. Hence, it is difficult to implement this technique in a system in which a memory band is limited.
The method of extending the polarity inversion period disclosed in patent literature 2 suffers a problem that flicker is readily viewed due to a long polarity inversion period. Since the “spatial frequency separation method” temporally divides spatial frequency components and displays them on respective sub-frames, in movie display with a quick motion, low frequency components are temporally shifted with respect to high frequency components due to their display time difference, and are often viewed as a tailing phenomenon.